Depending on the chosen elemental damage type, Chroma can be effective against all factions.
Using Toxin elemental damage in tandem with weapons modded for corrosive stats makes Chroma effective against the Grineer.
Using Electric elemental damage and activating elemental ward is a good way to thin a group of Corpus using weapons wth high damage output, as it reflects a percentage of damage back to the attacker in the form of an electrical arc.
Fire damage is good for crowd control, as it causes hostiles to panic and flail about, leaving them open to attack.
Using Cold elemental damage and activating Vex armor and elemental ward at the same time with greatly increase armor, as Vex Armor boosts armor whenever shields are hit and when Cold is selected, Elemental ward provides a marginal armor bonus.